Platies visibly sick, guppies dying

[Zuzkots]

Please help!
I'm having my first problem with fish since I got my tank. I'm sorry this is so long!
I added 2 female guppies and 1 female platy to my tank 10 days ago to fix a male/female ratio problem I had. I bought these at Pets At Home, all the fish in their tanks looked healthy. The only other thing I added to my tank are 2 java moss balls from eBay.
I also switched to an external filter a couple of days ago (I moved the media from the internal one to the external one and water parameters haven't changed since, testing daily).
Since I added the new fish, my other pregnant female platy started hiding in one of the ornaments, only coming out to eat. The red male always stays with her. I thought it was to do with her pregnancy or that she was intimidated by the new fish, until she started rubbing against everything couple of days ago. She has white spots on her but those don't look like growths, more like her colour rubbed off in places from scratching on things. The red male has a white area on his head (see the pictures).
On Friday I found a male guppy dead I examined his body but couldn't see any sign of illness. Well, I panicked and based on the platy's rubbing against things, I got an ich treatment (stupid I know) and treated the water yesterday, took the carbon out of the filter and slowly raised the tank temperature to 26'C. Since then, the platy stopped rubbing against things but still either hiding or hanging out at the top. The red male's swimming is a bit erratic today.
This morning my other make guppy looks like he's dying - lethargic, staying at the bottom, not eating, half of tail fin nipped off - I put him in a breeder net to protect him from other fish and turned the lights off). Other fish are looking and acting healthy. I've been keeping a close eye on my gouramis but they're not interested in the guppies at all.
I've no idea what's going on. Should I continue with the ich treatment? Or could it be velvet? Do a large water change? Or will that stress them out even more? I don't have a QT.
Any help or suggestions would be very much appreciated. Thank you!

Tank: 64l, cycled, planted, air stone
Filter: TetraTec EX600
4 platies (2m, 2f) + 1 fry
had 6 guppies (1m dead, 1m dying, 4f)
2 rubbernose plecos
2 dwarf gouramis (1m, 1f, very placid)
Water parameters:
pH 7.0
HRpH 7.4
Amm 0 ppm
Nitrite 0 ppm
Nitrate 10 ppm

 

[spiketooth]

Dont look or sound like ick. Ick is white spots and looks like grains of salt. I would say a bacteria infection. You can stop the treatment for ich, do a 50% water change then add a carbon filter to remove the rest of the ich meds, then removd the carbon filter add add meds are bacteria.

 

[Zuzkots]

Dont look or sound like ick. Ick is white spots and looks like grains of salt. I would say a bacteria infection. You can stop the treatment for ich, do a 50% water change then add a carbon filter to remove the rest of the ich meds, then removd the carbon filter add add meds are bacteria.

Thanks for the advice!
The guppy is not showing any signs of life anymore
I did a 50% WC and put the carbon filter back. I'll get new meds tomorrow, hopefully that'll help the rest of the fish.
Thanks again.